Getting a directory inside a .jar

Question

I am trying to access a directory inside my jar file. I want to go through every of the files inside the directory itself. I tried, for example, using the following:

<

Answer 1

Here is a solution which should work given that you use Java 7... The "trick" is to use the new file API. Oracle JDK provides a FileSystem implementation which can be used to peek into/modify ZIP files, and that include jars!

Preliminary: grab System.getProperty("java.class.path", "."), split against :; this will give you all entries in your defined classpath.

First, define a method to obtain a FileSystem out of a classpath entry:

private static final Map<String, ?> ENV = Collections.emptyMap();

//

private static FileSystem getFileSystem(final String entryName)
    throws IOException
{
    final String uri = entryName.endsWith(".jar") || entryName.endsWith(".zip"))
        ? "jar:file:" + entryName : "file:" + entryName;
    return FileSystems.newFileSystem(URI.create(uri), ENV);
}

Then create a method to tell whether a path exists within a filesystem:

private static boolean pathExists(final FileSystem fs, final String needle)
{
    final Path path = fs.getPath(needle);
    return Files.exists(path);
}

Use it to locate your directory.

Once you have the correct FileSystem, use it to walk your directory using .getPath() as above and open a DirectoryStream using Files.newDirectoryStream().

And don't forget to .close() a FileSystem once you're done with it!

Here is a sample main() demonstrating how to read all the root entries of a jar:

public static void main(final String... args)
    throws IOException
{
    final Map<String, ?> env = Collections.emptyMap();
    final String jarName = "/opt/sunjdk/1.6/current/jre/lib/plugin.jar";
    final URI uri = URI.create("jar:file:" + jarName);
    final FileSystem fs = FileSystems.newFileSystem(uri, env);
    final Path dir = fs.getPath("/");
    for (Path entry : Files.newDirectoryStream(dir))
        System.out.println(entry);
}

Answer 2

You can use the PathMatchingResourcePatternResolver provided by Spring.

public class SpringResourceLoader {

    public static void main(String[] args) throws IOException {
        PathMatchingResourcePatternResolver resolver = new PathMatchingResourcePatternResolver();

        // Ant-style path matching
        Resource[] resources = resolver.getResources("/Images/**");

        for (Resource resource : resources) {
            System.out.println("resource = " + resource);
            InputStream is = resource.getInputStream();
            BufferedImage img =  ImageIO.read(is);
            System.out.println("img.getHeight() = " + img.getHeight());
            System.out.println("img.getWidth() = " + img.getWidth());
        }
    }
}

I didn't do anything fancy with the returned Resource but you get the picture.

Add this to your maven dependency (if using maven):

<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-core</artifactId>
    <version>3.1.2.RELEASE</version>
</dependency>

This will work directly from within Eclipse/NetBeans/IntelliJ and in the jar that's deployed.

Running from within IntelliJ gives me the following output:

resource = file [C:\Users\maba\Development\stackoverflow\Q12016222\target\classes\pictures\BMW-R1100S-2004-03.jpg]
img.getHeight() = 768
img.getWidth() = 1024

Running from command line with executable jar gives me the following output:

C:\Users\maba\Development\stackoverflow\Q12016222\target>java -jar Q12016222-1.0-SNAPSHOT.jar
resource = class path resource [pictures/BMW-R1100S-2004-03.jpg]
img.getHeight() = 768
img.getWidth() = 1024